A semiconductor substrate is contained in every piece of electronics and widely used. In particular, a wide band gap semiconductor substrate is a material expected as a semiconductor substrate for a high-efficiency device contributing to energy saving and a power device. Among others, a diamond substrate is widely used not only as a semiconductor substrate but also for various tools (cutting tools such as a drill, an end mill, a milling cutter, a cutter, and a cutting tool, dice, jet nozzles for water or other fluids, and wear resistant tools such as a stichel), optical components (a window and a lens), and materials for electronic components (a heat radiating substrate), and importance thereof will further increase in the future.
Most semiconductors can be formed into a thin film, in a plate shape, or in a bulk shape with a vapor-phase synthesis method (hereinafter also referred to as chemical vapor deposition (CVD)).
In the vapor-phase synthesis method, a semiconductor layer is grown on a seed substrate composed of a seed crystal. The semiconductor layer can be used together with the seed substrate. Alternatively, the semiconductor layer may be separated from the seed substrate and only the semiconductor layer can be used for a product. In this case, since the seed substrate can be used again, manufacturing cost can be reduced.
PTD 1 (Japanese Patent Laying-Open No. 6-234595) discloses a method of alternately stacking a first diamond layer high in light transmission property and a second diamond layer low in light transmission property with a vapor-phase synthesis method, irradiating the stack with laser beams to have the second diamond layer absorb the laser beams, and separating the first diamond layer as a diamond thin plate.
PTD 2 (Japanese Patent Laying-Open No. 2007-112637) discloses a method of growing a first diamond layer low in light transmission property and a second diamond layer high in light transmission property on a substrate with a vapor-phase synthesis method to thereby obtain a stack, irradiating an upper surface or a lower surface of the stack with laser beams to thereby alter the first diamond layer, and peeling the altered first diamond layer through such treatment as heat treatment, electrochemical etching, or acid etching to thereby separate the second diamond layer.
PTD 3 (U.S. Pat. No. 5,587,210) discloses a method of forming a damaged layer composed of non-diamond carbon in a substrate by implanting ions into a diamond substrate, thereafter growing diamond on the substrate with a vapor-phase synthesis method, thereafter electrochemically etching the damaged layer, and separating the grown diamond from the substrate.
In order to reduce manufacturing cost, it is also effective to thinly slice a seed substrate for use.
PTD 4 (Japanese Patent Laying-Open No. 2011-60860) discloses a method of forming a reformed layer in a substrate by irradiating a front surface of the substrate with laser beams, thereafter etching the reformed layer, and slicing the substrate.
PTD 5 (Japanese Patent Laying-Open No. 2012-169363) discloses a substrate processing method of forming a reformed layer in a substrate by irradiating a front surface of the substrate with laser beams and thereafter splitting the substrate at the reformed layer or in the vicinity of the reformed layer.
PTD 6 (Japanese Patent Laying-Open No. 2011-60862) discloses a substrate slicing method including forming a reformed layer in a substrate by irradiating a front surface of the substrate with laser beams, thereafter providing a groove in the reformed layer, and peeling the substrate with the groove being defined as a starting point.